The IEEE standard for token ring data communication provides for the timing of signals and takes in account worse case scenarios of all physical layer conditions. IEEE Standard 802.5 "Token Ring Access Method and Physical Layer Specification" is particularly relevant. The physical layer conditions include all the possible conditions of the connection from the back of a work station to the network cable, travel of the signals over the cable, connection of the cable to a module in a concentrator, the electrical connection between the module and the backplane in a concentrator, and the subsequent electrical connections from the backplane to another module, to another cable and to another work station. A token ring adapter is used at the connections to the ends of the network cable and at the connections to the backplane. Each of the token ring adapters have a physical layer device and a MAC device. The physical layer device handles the physical layer of the token ring standard and the MAC device handles the data link layer of the standard. These two layers of the token ring standard are adjacent to each other and are very related. The IEEE standard is somewhat loose with regard to separating functions between the physical layer and in the data link layer.
Therefore electronic integrated circuit (IC) manufacturers often make a pair of integrated circuits, known as a "chip set" for handling the physical and data link layers of the token ring standard. The physical layer device IC and the data link or MAC device IC of a chip set are designed to compliment each other and to work together as a single unit to take care of all the functions and signals of the physical and data link layer of the IEEE token ring standard.
In order for a chip set to be widely used, the manufacturer of a chip set will design the chip set to conform to all the IEEE requirements, to be used in all parts of a LAN and to design the chip set to operate in worse case scenarios.
While this may be advantageous for sales of a chip set, it is often disadvantageous in situations where all the functions and safeguards are not needed. These extra functions and safeguards lower the performance in situations where the worse case scenarios will not be encountered. However, designing a chip set for only the circumstances of a particular situation is often uneconomical due to the high cost of designing a completely new chip set and the low number of situations needing that particular chip set. Therefore designers of LANs must make a compromise between using standard chip sets and foregoing any possible increases in performance, or investing a great deal of time and money in designing a chip set to take advantage of the particular circumstances of a particular situation. The advantages are usually not great enough to justify the expense.